Tunable magnetron tube



Sept. 22, 1953 F. H. CRAWFORD TUNABLE MAGNETRON TUBE Filed Jan. 3, 1946FIG.!

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INVENTOR FRAN 20 H. CRAWFORD yxe/M 2 Mail? ATTORNEY Patented Sept. 22,1953 TUNABLE MAGNETRON TUBE Franzo H. Crawford, Williamstown, -Mass.,assignor to the United States of America as represented by the Secretaryof War Application January 3, 1946, Serial 'No. 638,896

9 Claims.

This invention relates generally to ultra-high frequency oscillatortubes. More particularly it relates to an improvement in tunablemagnetrons permitting anode segments tobe unstrapped. I

In the developmentofoscillators of themagnetrontype numerous problemshave existed. One of these problems has been due to the fact that thisdevice has been subject to multi-rnoding and this inclination hasnecessitated the use of anode strapping. This imposed mechanicallimitation-upon the flexibility of its use and it added a structuralrequirement in its fabrication.

It is one of the objects of this invention therefore to improve theconstruction of magnetron l tubes by eliminating the use of anodestrapping without permitting the tube to become prone to multimoding.

In general this invention contemplates the use of a magnetron either ofthe type known to the art as a plural cavity magnetron, or of the typeknown as a vane type magnetron, combined with tuning elements which canbe controllably introduced in a conventional manner into the electricand the magnetic fields of the resonant cavities formed in the magnetronso as to increase or decrease simultaneously the capacitance and theinductance of the resonant cavities, thereby altering theinductance-capacitance (LC) product of the cavities and thus alteringthe frequency of oscillation. The said associated means, however, are ofnovel design which avoids the need of anode strapping.

Other objects, features and advantages of this invention will suggestthemselves to those skilled in the art and will become apparent from thefollowing description of the invention taken in connection with theaccompanying drawing in which:

Fig. 1 is a sectional view of a vane type magnetron having tuning means,the sectional view being taken in a plane which passes through the anodestrap and is parallel to the ends of the cylindrical body of themagnetron;

Fig. 2 is a corresponding sectional view of the same type of magnetronas shown in Fig. 1 showing an embodiment of the novel type of the tuningmeans; and

Fig. 3 is a sectional view, taken in a plane passing through the axis ofthe cylindrical body of the magnetron along line 3, 3 of Fig. 1, of abroken away top portion of an embodiment of this invention, showing thesupporting means of the tuning elements.

The specific form ofmechanicalstructure employed to support and to movethe tuning means is not the major part of this invention but isdescribed in my copending application Serial No. 638,895, filed January3, 1946 and entitled Tunable Magnetron Tube.

Referring now more particularly to Fig. 1, case it, vanes H, strap I2,cathode l3, inductance loading slugs l4 and capacity-varying elements l5are parts of a vane type of tunable magnetron. The space betweenadjacent vanes is called a cavity resonator.

An inductance loading element, such as slugs M, when it is inserted intoa resonant cavity in a part of the cavity which oifers a relativelylarge value of lumped inductance, reduces said value of inductance andthus effects the fre quency of resonance. pacity-varying element, suchas an element it, into the part of a resonant cavity which offers arelatively large value of lumped capacitance is capable'o-I' increasingthis lumped capacitance and also efiiects the frequency of resonance. Itis therefore conventional art to employ simultaneously both inductanceloading elements and capacity-varying elements arranged so that whenmoved they quantitatively change the inductive and capacitive parametersin the same direction.

Referring to Fig. 2 it can be seen that the inductance loading elementsand capacity varying elements which are installed in adjacent cav itiesin this improvement are of unequal physical dimensions and thereforehave unequal inductive loading and capacitive reactance varying effects,respectively, while those of alternate cavities are equal andthat anodestrap 52 is not used. It has been found that the use of non-symmetricalelements, that is, elements having unequal impedance varying effects inadjacent cavities lessens the tendency to multimoding to such an extentthat anode strapping is unnecessary. This permits a simplification inthe construction of magnetrons and greater latitude in selectin thesizes and dimensions of other internal elements. It is obvious thatnon-symmetry can be achieved in a variety of ways including usingelements having diiierent sizes and diiierent shapes or using elementscomposed of different materials. Moreover the same principle is fullyapplicable to magnetrons which are not of the vane type such, forexample, as multiple cylindrical cavity magnetrons, and it is applicablewhether the capacity-varying elements are composed of a conductive or ofa dielectric mater1a The insertion of a ca- Referring now to Fig. 3 itwill be seen that inductance loading slugs It are connected at theirupper ends to rods [6 and that capacityvarying elements l5 are connectedat their upper ends to rods l1. Rods l6 and I! are part of the meansused to control the positions of these elements. In length rods I! areshorter than rods I6. This difference length is such that the beginningsof slugs I4 occur in the same plane as the ends of elements Hi. Theupper ends of all rods l6 and [1 are fastened into structure it whichhas substantially the shape of a large washer whose outer diameter isapproximately equal to the outer diameter of the magnetron. Pairs ofrods, each pair consisting of a rod [6 and a rod [1, are free to moveinto and out of case In through holes =19. Each hole It is positionedabove a cavity resonator of the magnetron and is large enough so thateach such pair of rods fit through without touching case [[3 at anypoint. Fastene'd above holes 1:9 with airtight junctions at one 'of theends of each of them are .Syipnons 2c. The other ends of sylphons 20 aresimilarly attached to structure IB, In this way rods H3 and "H are freeto be pushed into or withdrawn from case 16 while a high vacuum can beand is preserved within case it and, of course, Sylphons 20.

While there has been described what is at present considered to be thepreferred embodiment of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention.

The invention claimed is:

1. A tunable magnetron comprising a plurality of cavity resonators,frequency adjusting means including a plurality of inductance loadingconductive elements and a plurality of dielectric insert elements, saidinductance loading elements and said "dielectric insert elements beingappreciably unequal in reactance varying properties in adjacentcavities, all of said induc'tan'ce loading :and all of said dielectricinsert elements being adjustably supported within the resonators ofsaidmagnetrons.

2. A. tunable evacuated magnetron comprising a plurality of cavityresonators, frequency adjusting means including a plurality ofconductive capacitative insert elements, said elements being appreciablyunequal in size in adjacent cavities and means adjustably supportingsaid elements within said cavity resonators.

3. A tunable evacuated magnetron comprising a plurality of cavityresonators and frequency adjusting means including a plurality ofinductance loading conductive elements, some of said elements beingappreciably unequal in size in adjacent cavities and means adjustablysupporting said elements within said cavity resonaors.

l. A tunable magnetron comprising'a plurality of cavity resonators andmeans including inductance loading conductive elements in two of saidresonators for adjusting the inductance of said two resonators, saidelements being appreciably unequal in size to avoid multi-moding,whereby the oscillation frequency may be varied.

5. A; tunable magnetron comprising a p1urality of cavity resonators andmeans including capacitance-varying insert elements in two of saidresonators for altering the capacitive reactance of said two resonators,said elements being appreciably unequal in size, whereby the oscillationfrequency may be varied.

6. A tunable magnetron comprising a plurality of cavity resonators andmeans for varying the oscillating frequency of said magnetron, saidmeans including inductance loading elements in at least two of saidresonators for adjusting the inductance of said two resonators, said twoelements being appreciably unequal in inductive loading effect to avoidmulti-moding.

'7. A tunable magnetron comprising a plurality of cavity resonators andmeans for varying the oscillating frequency of said magnetron, saidmeans including capacitance varying insert elements in at least two ofsaid resonators for altering the capacitive reactance of said tworesonators, said elements being appreciably unequal in capacitancevarying effect, whereby multi-moding is reduced.

8.. A tunable magnetron comprising a plurality of cavity .resonators andmeans for varying the oscillating frequency of said magnetron, saidmeans including impedance varying insert elements in at least two ofsaid resonators, said two elements being appreciably unequal inimpedance varying effect.

9. A tunable magnetron comprising a plurality of cavity resonatorshaving the same dimensions, and means resonating at least one of said.FRANZO H. CRAW FORD.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,281,935 Hansen May 5, 1942 2,408,234 Spencer Sept. 24, 19462,449,794 Steele Sept. 21, 1M3

